Global Agriculture As Part of the Climate Solution

For quite a while, agriculture was dismissed as a possible way to mitigate climate change, because it’s where our food comes from, and we can’t live without food. From this obvious fact came the misinterpretation that we couldn’t cut agricultural greenhouse gas emissions without threatening food security.

That was important, but it still left out the emissions that came directly from the food system, not just from the pressure that system exerts on natural ecosystems. Those emissions come from extremely diverse sources – e.g. using petroleum to produce fertilizer, transporting vegetables thousands of miles, throwing out milk that has spoiled, and the stomachs of beef cattle producing methane – and it wasn’t clear which of the many possibilities had the biggest potential to mitigate climate change.

Potential greenhouse gas mitigation from agriculture, in millions of metric tons of CO2 equivalent per year in the year 2030, relative to the baseline level. Source: Dickie et al. 2014, Table 2 (top part only).

The big winner – or rather, what would make humanity the biggest winner, if we face up to the challenge — is shifting dietary trends. That is, changing our food consumption patterns, with a potential to reduce emissions by 2150 million metric tons of CO2 equivalent (Mt CO2eq) in the year 2030, has by far the greatest potential, amounting to about twice as much as any other. Second at 1135 (if you take the high estimate of it) is increasing soil carbon sequestration on cropland (but this is just 435 Mt CO2eq/year if you take the low estimate). Next come production-side approaches to reducing enteric fermentation – that methane from the stomachs of cows and other ruminant livestock – at 940, and then reducing wastage in the food chain, at 750 Mt CO2eq/year.

If these terms seem a bit too wonky, here’s what we’re talking about in terms of what’s on our dinner plates today:

Greenhouse gas emissions by agricultural commodity, in million of tons of CO2 equivalent per year. These emissions include (in gray cross-hatching) emissions from LUC (land use change – nearly all from tropical deforestation), peat soil degradation, and fires that are caused by beef, palm oil, and soybean production, as well as the direct emissions from production across the globe (in solid colors, depending on where the commodity was grown). Source: Dickie et al. 2014, Figure 4.

Clearly, the biggest current source is beef, with about three-quarters of its total of 2000 Mt CO2eq/year from direct emissions (that methane from cattle again) and a quarter from the deforestation that it drives. Taken together, the ruminants (beef cattle, water buffalo, sheep, goats, and dairy cattle) contribute over 90 percent of the emissions from livestock. Beef cattle alone cause about the same amount of global warming pollution as all the world’s crops combined. So, as the report makes clear, the biggest component of the “shifting dietary trends” in the first graphic, is shifting away from beef.

This report is an important step forward in dealing with global warming pollution from the land sector – and I don’t say that just because it reinforces some of the things I’ve written myself in various journal articles and reports. (Although I admit, it’s always reassuring when colleagues look at the evidence independently and come to the same conclusions.) Here are some of the ways that this study goes beyond previous work, including mine, in important ways:

It looks at allthe potential solutions, on both the supply side – what agriculture produces and how it does it, and on the demand side – what people eat, and how it gets to our plates through the global food web. And as you can see from the first graphic, the demand side approaches of shifting diet and reducing waste have more potential than either carbon sequestration or emissions reductions on the supply side.

It puts numbers on the different possibilities, so that we can see where the biggest opportunities lie. And it does this while fully taking into consideration the uncertainty in many of those numbers, leading us to the necessary caution but without paralyzing action because we need more research (as we always do!)

It separates out emissions and mitigation potential not only by potential actions that could be taken, but also by country. This is critical because of the differences among nations in their sources of agricultural emissions – palm oil-driven deforestation in Indonesia., inefficient production, and overuse of fertilizer in China, cattle for beef in the U.S. but for dairy and as draft animals in India – and the importance of this diversity for the efficiency and equity of potential climate solutions.

It presents its results in awesome detail. The main report is 146 pages long, and it has two technical appendices of more than a hundred pages each on current agricultural emissions and on their estimates of 2030 mitigation potential.

With the study of Dickie and colleagues, we now have another new science-based assessment – independent of the IPCC Working Group 3 report, about which I blogged a few weeks ago – that gives us the information needed for effective climate mitigation in the land sector. This is what we need to act, in all parts of the global food system.

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